Continuous casting



Jan. 9, 1945. J. s. SMART, JR, ET AL 2,367,148

CONTINUOUS CASTING Filed Nov. 11, 1942 fr Y, mm m E WJM 4 52 PatentedJan. 9, 1945 CONTINUOUS CAS'lIlfIG John S. Smart, Jr., Scotch Plains,and Albert A.

Smith, Jr., Metnchen, N. 1., assignors to Amerlcan smelting and RefiningCompany, New York, N. Y., a corporation of New Jersey ApplicationNovember 11, 1942, Serial No. 465,190

8 Claims.

This invention relatesto the art of continuous casting and moreparticularly to an improved mold and method for producing continuouscast metal shapes of uniformly high density which are free fromobjectionable surface cracks and imperfections. I

When casting metal, such as copper, brass and the like, wherein themolten metal'is introduced into one end of a die or mold having thedesired shape and passed downwardly therethrough concurrently as it ischilled to form a solidified cast shape which is continuously withdrawnfrom the ent, to a large extent, upon the proper location of the pointor zone in the mold where initial congealing of the molten metal takesplace. Premature congealing of the molten metal above the zone where themaximum rate of heat extraction is being eifected results in theformation of pronounced checks or cracks in the outer surface portion ofthe casting. In extreme cases freezing" of the apparatus and stoppage ofthe process ensues.

Where the cross-sectional area of the rod being cast is relatively largethe point intermediate the ends of the mold where initial solidificationopposite end of the mold, it has been observed 4 that the production ofsound castings is dependof the liquid metal takes place tends to occurat or near the proper location so that its control is less of a problem.However, when casting relatively small diameter rod, for example, lessthan three inches, control of the point or zone where initialsolidification occurs becomes increasingly more important as thediameter of the cast rod is decreased. With small rods, the ratio of thediameter of the rod to the length of the mold is proportionately lessand molten metal is required ing zone solidifies a fragile skin-likeouter portionwhichshrinks away from the side walls of the mold and isruptured when subjected to the hdrostatic head pressure and frictionalor mechanical stresses incident to the casting process.

Fracture of the newly formed outer skin-like shell also is brought aboutwhen this thin shell shrinks away from the mold wall andis reheatedsufllciently, by the molten metal in the central portion of the casting,to cause it to expand and again contact the mold wall setting upfrictional stresses which the thin shell is unable to withstand. Thesebreaks appear as checks or cracks in the outer surface of the cast shapeand the checking cycle is often repeated periodically as the castingprocess proceeds.

It is the principal object of this invention to overcome thesedifllculties" by devising a mold and method of casting whereby thelocation of the metal congealingzone can be predetermined and thefreezing of the metal controlled to avoid the formation of castingshaving surface defects.

According to the invention there is provided a mold which during usefunctions to prevent the molten metal from losing its latent heat untilit reaches the zone of high heat extraction capacity. Provision isalsomade whereby after the molten metal reaches this zone it is allowed toflow laterally from a central source of supply toward the side walls ofthe mold while being blocked or otherwise prevented from rising above apredetermined point in the mold, such point being below that at whichinitial solidification of the molten metal would occur under otherwiseidentical casting conditions. During casting, themold and associatedparts of the casting apparatus are kept filled with the molten metalbeing cast. Concurrently, as the liquid metal reaches the desiredlocation in the mold where solidification of the metal is to beinstituted, it is immediately subjected to a high rate of heatextraction. In this way a thick heavy shell of solidified metal isinitially formed around the casting shape which is strong enough towithstand the hydrostatic head pressure of the molten metal andfrictional stresses imposed upon it without ruptaken in connection withthe accompanyingdrawing. The drawing shows, diagrammatically.

a sectional elevation of one form of apparatus in accordance with theinvention and which may be employed in practicing the-new methodthereof; the part of the furnace utilized for retaining molten metalbeing shown partly broken aw.

Referring to the drawing more in detail, the numeral Ill indicates,generally, a reservoir or casting furnace section for holding moltenmetal to be cast, as shown at I2. Suitably arranged in the fioor of thereservoir I is a mold l4 into which molten metal from the reservoir isintroduced during the casting process.

In continuously casting copper, for example, molten copper is treated inaccordance with the usual practice to render it substantially gas-free,and of the desired composition, prior to introducing the metal into themold. Turbulence of the molten metal is avoided by positioning the moldll in the fioor of the furnace at a point remote from the charging end.Further, the hydrostatic head of molten metal is kept substantiallyconstant. These factors may be controlled in amanner known to thoseskilled in the art, in which connection reference may be made toBetterton and Poland Patent No. 2,195,809, granted April 2, 1940.

The mold I4 is made of refractory material which is suitable anddurable, such as, dense graphite, metal, or the like. Appropriately themold may be in accordance with Poland and Lindner Patent No. 2,136,394,granted November 15, 1938. A central tubular member 18 is provided asshown, through which molten metal is conducted from the reservoir Illdown into the mold or forming die portion 20. Where desired, this tubemay be provided with valve means, not shown, for regulating the flow ofmolten metal therethrough, otherwise the column of metal defined by tubeI8 and portion of mold l4 will be automatically replenished from thesupply 12 in response to the downward movement of the column as thecasting is withdrawn from the mold. Surrounding the die portion 20 ofthe mold there is positioned a water cooling jacket 22 through whichwater is circulated to provide a cooling or refrigerating zone by whichheat is extracted from the column of molten metal to progressivelysolidify it from its periphery toward its central axis as indicated inthe drawing. Cooling water is conducted to and from the jacket 22 from asuitable source of supply,

not shown, by means of the conduits 24 and 25 respectively.

In order to prevent the molten metal from beginning to freeze orsolidify before it reaches the desired point in the cooling zone of themold, the delivery tube I8 is made to extend down to the point where ahigh rate of heat extraction can be effected and the annular spacebetween the tube and the inner wall of the mold is filled with heatinsulating material 28. Alundum cement, for example, or other suitablerefractory material may be used for this purpose. This is either rammedor tamped in place while moist, then dried and fired, or inserted as apreformed shape. Any other suitable method of insulating the tube fromthe mold wall may be employed. By arranging the mold and associatedcasting parts in this manner, the point in the mold where it is desiredto initiate solidification of the molten metal can be readilypredetermined. Thus freezing of the metal to form the cast shape iscontrolled so that a thick shell of metal can be solidified during theinitial stage of forming the casting shape.

In the scheme illustrated, molten metal flowing into the mold I4 isprevented from-coming in contact with the mold above the point selectedfor initial solidification in the refrigerating zone formed by thecooling water jacket 22, by means of the heat insulating filler material28 and tube l8, the latter serving to constrict the downwardly movingcolumn of molten metal in cross-section to immediately above theselectedpoint while the lower portion of the filler material forms a wall 30extending from the mouth of the delivery tube l8 to the side walls ofthe mold, thus mechanically blocking-01f the upward flow of liquid metalat the desired location.

Preferably, most of the heat is extracted laterally from the centralcore of the casting through the walls of the mold adjacent the watercooling jacket, but a minor amount may be extracted upwardly andoutwardly through the ceiling wall 30 as the molten metal leaves the endof the tube l8 and fiows laterally toward the sides of the mold. Thesize of the bore forming the tube I8 is such as to provide for delivery'of enough molten metal to maintain the mold filled at all times duringcasting-and will vary depending on the casting speed employed and thedesired diameter of the rod being cast.

By confining the point or zone of initial freezing at theproper locationwith respect to the fluid cooled section of the mold, and maintainingthe mold filled during casting with avoidance of turbulence, asdescribed, considerably higher casting speed than considered feasibleheretofore can be used. Sound copper castings having exceptionally highdensity, for example having a specific gravity of 8.95+, are readilyproduced by the process of this invention. Instead of forming arelatively long thin solid metal phase at the interface representing thecongelation point of the molten metal, there is produced a relativelyshort, thick heavy shell of solidified metal. This latter thick shell,unlike the former, possesses suificient strength to withstand thetemperatures and stresses involved during the continuous casting processwithout remelting, rupturing or deforming as it is moved downwardlythrough the mold.

While the invention is particularly adapted to the continuous casting ofcopper or copper alloys, it will be understood that the principlesthereof are applicable generally to the casting of other non-ferrous aswell as ferrous metals and alloys which present problems similar tothose encountered in,continuously casting copper or its alloys.

What is claimed is:

l. A process for continuously casting metal which comprises introducingmolten metal into one end of a mold, continuously withdrawing solidifiedmetal from the other end, maintaining a cooling zone in one portion ofthe mold, conducting molten metal downwardly into said mold through acentral delivery tube to the point where it is desired thatsolidification of the molten metal take place to form a cast shape, andabruptly blocking the rise or reverse fiow of molten metal contiguousthe walls of the mold adjacent said point to force the molten metal toflow laterly from the lower end of said central delivery tube toward theside walls of the mold while concurrently extracting heat from the 6;In"continuous "casting ofacoppeeerod ofmining the po'int'or'zcne'in the'nio'ld where initial freezing of the molten metal is to take place.conducting the molten metal downto this zone through a central deliverytube while the same is prevented by heat insulating material arrangedbetween the tube and mold side walls from .los- 1 ing heat sufllcient toinstitute solidification, thereafter causing the molten metal to fiowlaterally from the lower end of the tube toward the side walls of saidmold, abruptly obstructing the upward rise of molten metal in the moldat the point where initial freezing of the molten ,metal is to takeplace, and simultaneously sub- -jecting the molten metal when reachingsaid point to a high rate of heat extraction to cause less than threeinches in diameter wherein molten metal is conducted from a supplythereof into one end of an open end mold having the desired shape andpassed downwardly therethrough concurrently as the metal is chilled toform a solidified cast shape which is continuously withdrawn thesolidification of a thick shell of metal which forms the outermost partof the-casting during the initial stage of the continuous castingprocess.

3. A process for continuously casting metal comprising introducingmolten metal into one end of a mold, continuously withdrawing solidifiedmetal from the other end, providing a cooling zone along a portion ofsaid mold, delivering the molten metal to the cooling zone of the moldthrough a restricted opening while preventin initial congelation untilit has passed through said opening, maintaining said mold and associateparts filled with molten metal. to avoid turbulence during casting, andabruptly blocking reverse fiow of the, molten metal thus delivered inthe mold at said cooling zone where initial freezing of the molten metalis to take place a while subjecting the molten metal flowing into saidcooling zone portion of the mold to a high rate of heat extraction tobring about the solidification of a thick outer shell of metal duringfrom the opposite end of the mold, the improvement consisting inproviding the inner wall of the mold with an annular abutment whichextends inwardly therefrom towards the central cavity of themold,thereby defining the upper limit of contact of the molten metal with themold side wall arranging a cooling water jacket around the outside ofsaid mold adjacent the annular abutment sectionof the mold, circulatingwater therethrough to extract the heat rapidly from the molten metalimmediately upon its flowing in contact with the side walls of the moldcontiguous with said annular abutment causing the initial freezing of athick outer shell of solidified metal during formation of the castshape, and

insulating said molten metal against loss of heat sufiicientto bringabout solidification while the metal from losing sufilcient heat tocause formation of the cast shape as the same is continuously beingwithdrawn from said mold.

4. In continuous casting mechanism, a reservoir for holdingmolten metal,a mold for receiving molten metal from said reservoir which is incommunication therewith, cooling means surrounding a portion of saidmold for congealing metal introduced therein, said mold having aninwardly extending annular abutment forming a molten metal tightjuncture with the side walls of said mold and arranged adjacent saidcooling means for limiting the upward fiow of molten metal contiguouswith the side walls of said mold during casting to bring about rapidsolidification of said molten metal adjacent and immediately below thejunction of said abutment and mold side walls whereby there is formed athick ,walled casting which can be withdrawn from the outer end of saidmold as a continuous cast shape without rupturing.

5. A mold for casting metal by continuously supplying molten metal toone end thereof and continuously withdrawing solidified metal from theother end thereof characterized in that the interior bore of said moldis provided with an annular abutment whichrextends inwardly from theside walls of said mold for limiting the rise of molten metal above apredetermined point where initial freezing of the molten metal is totake place, and means comprising a fiuid cooling jacket arranged aroundsaid mold adjacent said point for providing a rapid rate of cooling tosolidify athick wall of metal aroundthe outing,

during the initial formation of the cast shape.

it is being conducted from the receptacle into said mold and in contactwith the side walls of the mold adjacent said abutment.

'1. In apparatus for continuously'casting metals, the combination with areservoir for molten metal, an open-ended, vertically-disposed mold forreceiving molten metal from said reservoir into its upper end anddischarging the casting from its lower end, and cooling means forsolidifying metal in the mold, of means contiguous with the inner moldwall denying molten metal access to said inner wall'above apredetermined point, said point being below that at which initialsolidification of the molten metal would occur under otherwise identicalconditions of casting, and insulating means precludingall-solidification of metal in the mold above said predetermined point.

8. In continuously casting metals by confining 4 molten metal as adownwardly moving column, directing the column through a cooling zonewhereby heat is extracted to form the casting by progressivelysolidifying the metal from the periphery of the column towarditscentral' axis,

and replenishing the column with molten metal from a supply thereof inresponse to the down ward movement of the column, the method ofinitially solidifying the molten metal at the periphery of the columnasa relatively thick shellv diately below the selected point isinitially, solidified as a relatively thick shell constituting the outerportion of the cast shape.

JOHN 8. SMART, JR. ALBERT A. SMITH, JR.

